1. Field of the Invention
The presently disclosed subject matter relates to a method for creating a color profile, and particularly, to conversion processing technology of a color image signal to be used in image formation of a color image formed on a medium by using an ink containing one or more kinds of ink of specific colors.
2. Description of the Related Art
As a method for managing colors in offset printing, a color management system using an ICC profile is known. ICC is an abbreviation for International Color Consortium.
The color management system using an ICC profile creates a color chart including a patch corresponding to respective signals of cyan, magenta, yellow, and black, and a patch corresponding to a signal created by combining at least two kinds of signals of cyan, magenta, yellow, and black, and allows the color chart created to be printed. Then, a colorimetric value of the color chart printed on a medium is acquired to create a color profile that describes a conversion relationship between a signal value of each of cyan, magenta, yellow, and black, and a Lab value corresponding to a colorimetric value of the signal value.
In creation of a color profile in a case of image formation using four-color ink, if ink of each of the four colors is used at a usage rate of 100 percent, a color patch is printed with an indication of the usage rate of 400 percent.
In image formation by offset printing and an electrophotographic method, a chart including a color patch at a usage rate of ink of 400 percent can be printed without problems. Unfortunately, there is a limit of the amount of ink that can be absorbed into paper used as a medium in image formation by an ink-jet method. In general, paper used in an image forming apparatus by the ink-jet method is only available for printing of a color patch at a usage rate of ink up to about 200 percent to 250 percent.
Thus, an image formation by the ink-jet method uses image processing that applies limitation of a total amount of ink.
Here, the usage rate is a scale indicating the amount of ink usage, and is expressed in percentage according to a form of the ICC profile. The usage rate is indicated at 0 percent if no ink is used, and at 100 percent if ink is used up to a maximum.
Image processing applying limitation of a total amount of ink includes processing in which cyan ink, magenta ink, and yellow ink are substituted with black ink by GCR processing so that the amount of the cyan ink, the magenta ink, and the yellow ink is reduced to limit a total amount of the ink.
The GCR processing is also called gray conversion in which cyan, magenta, and yellow are removed from a gray portion to express gray by only gradation of black. GCR is an abbreviation for gray-component replacement.
In addition, image processing applying another limitation of a total amount of ink includes a method of processing each of a signal of gradation of a single color, and a signal of two or more colors, so that ink for each of the signals is within an upper limit value of a total amount of each of the ink.
Japanese Patent Application Laid-Open No. 2014-068198 describes a method and program for creating a table of limiting a total amount of a color material, the table being used to convert a signal value to limit the amount of ink to be applied to a medium. The method and program for creating the table of limiting a total amount of a color material described in Japanese Patent Application Laid-Open No. 2014-068198 allocate a total amount of ink to a division of a color reproduction area according to an upper limit value of the total amount of ink to determine limitation of a total amount of ink of the whole of the color reproduction area. The color material described in Japanese Patent Application Laid-Open No. 2014-068198 includes ink and a toner.
In recent years, a specific color other than process colors, such as cyan, magenta, yellow, and black, is additionally used in an output device, such as an image forming apparatus. The specific color includes orange, green, violet, and the like.
Japanese Patent Application Laid-Open No. 2007-329737 describes an apparatus of creating definition of color conversion and a program of creating definition of color conversion, using orange and green in addition to process colors of cyan, magenta, yellow, and black.